Protein S degradationin vitroby neutrophil elastase

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Abstract
Human protein S is degraded by neutrophil elastase. The characteristics of cleavage are compared in a purified protein S preparation, a concentrate of vitamin K-dependent proteins (PPSB) and in normal plasma as well as in a-proteinase inhibitor (cePI)- deficient plasma. Elastase incubation of purified human protein S (molar enzyme-to-substrate-ratio 1: 5500-1: 55) reduces the molar mass of the native protein S (81-83kDa) to about 79kDa by cleavage of a small peptide. Incubation with very high elastase concentrations (molar enzyme-to-substrate-ratio 1: 5.5) completely degrades protein S into small fragments. The elastase incubated protein S has a higher isoelectric point than the native form (Ip5.9 vs. 5.3). Protein S in a PPSB coagulation factor concentrate is degraded in the same way as isolated protein S. By immunoblotting also smaller split products of molar masses between 34 and 70kDa are demonstrated. In normal plasma protein S is not degraded by elastase concentrations up to 14 μmol -1. In plasma of a patient with a,-proteinase inhibitor deficiency protein S can be degraded by elastase. The native 82kDa protein is degraded to a 72kDa protein. PEG precipitation of the protein S- C4b- binding protein-complex shows that elastase predominantly splits the free protein S.